Directional coupler



June 9, 1953 s. SENSIPER DIRECTIONAL COUPLER Filed Jan. 25, 1949 xrxxIII? llrr XXIX xxlx INVENTOR SAMUEL SENS/PER Patented June 9, 1953UNITED STAT DIRECTIONALTCOUPLEB Samuel Sensiper, Cambridge, Massassignor to The Sperry Corporation, Great Neck, N. Y., a corporation ofDelaware 1 Application January 25, 1 949, senrm). r2591 The presentinvention relates to electromagnetic energy couplers between ultra highfrequency energy transmission lines, such as wave guides, coaxial lines,or the like, and in particular relates to directional couplers betweentwo such ultra high frequency transmission lines.

In order to connect measuring apparatus to an ultra high frequencyenergy transmission system, some means of radio frequency energycoupling must be provided. Such coupling means operate independently ofthe standing waves which may exist in the transmission line, and theamount of power which is extracted from the transmission line shouldpreferably be a definite fraction of the power which is to betransmitted along the main transmission line. To obtain theseadvantageous conditions, it ishighly desirable that the coupler operatein such a manner that an electromagnetic wave travelling in a singledirection along the main line induce a wave travelling in a singledirection along the coupling line. Likewise, a wave travelling in theopposite direction in the main line should induce a wave travelling inthe opposite direction in the coupling line. 'A coupler which has theseproperties is known as a directional coupler. The performance of adirectional coupler may be described in terms of three quantities:

(1) Attenuation The attenuation of a coupler is the strength of thetravelling wave in the main line relative to the strength of thetravelling wave which it induces in the auxiliary or coupling line. Thisis a power ratio, usually expressed in decibels.

(2) Directi'uz'ty o (3) Bandwidth The bandwidthover which the couplerpro- I 3 Claims. (01. 178-44) Typical directionalcouplers of thepriorarti'or coaxial lines and wave guides are shown by Tervides maximumdirectivity with minimum. atv tenuation is important in manyinstallations. It is particularly desirable to'iprovide a wide bandwidthof operation to extend the useful operating range of the coupler so thatone coupler can do the same job that a number of difierent couplersformerly did.

man in Radio Engineering, published 1947, by McGraw-Hill, pages 112 to141. One type or these couplingscomprises a pair of parallel wave guideshaving two couplingholes spaced one-quarter wavelength apart. In thesecondary wave guide, propagation is reenforced in a desired directionand cancelled in theopposite direction dueto the half wavelengthdifference in path of travel; The disadvantages of this type coupler isthat it is frequency sensitive, and has a narrow 'usee ful bandwidth dueto the quarter wavelength limitation. Y i Another typical prior artcoupler shown in the Terman reference is the single hole, or Bethehole,coupler in which both electrical and magnetic coupling takes placethrough the same opening. In this type coupling the electric fieldproduces energy flow in both directions in the secondary line, where thewaves in the secondary line travelling away from the coupling point areessentially in phase at the coupling point; the magneticfield producesenergy fiow in both directions in thesecondary line, but the waves inthe secondary line travelling away from the coupling point areessentially 180 out of phase at the coupling point. The magneticcoupling 1s proportional to the cosine .of the angle at which theprimary and secondary guides cross, whereas the electrostatic couplingis independent o1 this angle. Therefore the ratio of the couplings maybe controlled so that they reenforce each other in one directionandcancel each other in the opposite direction by adjusting the anglebetween the primary and secondary guides. Good dlrectivity in thesecondary guide is obtained at an angle of approximately 63 degrees.This single hole coupler has the disadvantage of havmg a bulky andinconveneint wave guide joint due to the required large angle betweenthe guldes. The coupler'i s merely a single hole and there are noparameters to adjust.

Accordingly, the principal object of the invention is to provide animproved wide band directional coupler for ultra high frequencytransmission lines.

Another object of the invention is top'rovide an improved directionalcoupler which is not frequency sensitivei a Another object of theinvention is to provide a directional coupler having substantiallyindependent magnetic and electric coupling.

Another object ofthe' invention is to proand the magnetic cou ling byeslots; opening;

Both or these couplings are in the same trans! verse plane of theguides, and. they are substane tially independent of each other. Thus,the frequency sensitive space factor of a multi hole; coupler iseliminated. In the present invention n9: irequencysensitiv ty-res ltsfrom; ila eeparation; I v

he. fact. ...at the ele tric; and. ma ih tieplihgs. are subs t ally indp ndent? prov d s parametersforz a j s ment for frequ ncy i sensitivity.V V

The single, hole, or, Bethe directional coupler is, W611..K QWI in the,art, and. i analyzed in the Principles oiQBadaL, by the M.. I. Tl. Radarcho S Li, hublished sc Mc aw-Hill. chanter 10, page 33, but t will bebriefly reviewed here for thepurpose. of explaining the,presentinvention.

"Figs. lA-lC illustrate a conventional single hole or Bethe directionalcoupler, Fig. in being the side view showing thc main. and. auxiliarywave guides I and 2, whichfare joined, togetheralong' their wi'defside;and; the single coupling hole 3. The electric field is illustrated bythe electric vectors 4: and the direction of energy flow in the mainguide I shown by the arrow 5'. The-electric vectors 4 fringe through thehole 3 and excite the auxiliary guide 2 in; both directions as shown bythearrowEA.

Fig: 1B is the same side view ofthe guides showing the portion of themagnetic field, illustrated by the dots and? crosses, which istransverse to thelongitudinal axis of the guides Ij and 2,. This:magnetic: field creates an electric field I across the couplingrholetdue to the charge 4 is the cross-section of Fig. 2A showing how probe I5is mounted. Probe I5 is preferably insulated as by washer II.

Fig. 2C shows the action of the probe I5 coupling the electric vectorinto the auxiliary guide I2. The probe I5 acts very much like an antennaexciting waves in the auxiliary guide I2. in both directionsas;show,n-.by-:arrows-:Eni The slot l4 couples the magnetic field intothe. auxiliary guide I2 in the same manner as the single hole coupler ofFigs. lA-1C. However, the fringing of, thfieldqtric fields is minimizeddue to the narrownessof" the slot.

Therefore, the; present invention acts similartn. the. single holecoupler but has the advantages. of? the additional probe which provides(381 113 parameters, such as size of probe and slot magnitudes of thecoupled fields.

currents 9 caused by; the; magmaticfields which flow; alongthe walls of;the. guides. This excitation. results, i waves travelling in. bothdirections -as; shown; by" anrow; Ear and E1 2 butthe phasehf h leo riofields is pp site; as shown. by the electric: vectors: I8.v and I9.

Fig. 1C showsthe two coupled. electric field'sof Figs. 1A and} 1Bsuperimposed, and illustrates that they reenforce; each other 11 he eand tend to cancel each; other to the; right, thereby prod ing h d redirec io al; Wave. A previously. mentioned. the two fields do. not: com-.pletely cancel and it is necessary to skewthe longitudinal axes of theguides to thereby vary the magnetic. coupling for complete cancellai Thepr sent. inrention. obta ns this; can;- ell oh. without skewing the:-guides.

Fig. 2A illustrates the directional. eouplergqof the present, inventionwhich, operates. Similarly to the conventional single hole coupler. QfFi .5. lA-lC'. It comprises main and. auxiliary wave guides II and t2,direction or power f ew being shown by the. arrow I3, a slot- I4, anda,probe I5 coupling thejtwo. guides being in the same n rse. plan r lat reto the guide 2 and their spacing for choosing of the relative Byproperly choosing the size of the slot I4, probe I5, the cahgel at on ofe fie s; the; u iliary 7 gu hd; he ore direet vi v max e; Q -ta' d, w hecut sk w n he: wave. guides.- t n. inconv nient.

n le. uch. as is requ ed; e; 0ll ritismalv singleholecoupler. '1 Theprobe; may. be made; justable by making it ortelescoping portionsyasshown in Fig; 2D; I

The advantage is that themagnetic and electric coupling adjustments havebeen; separated; This, invention avoids frequency sensitivity re,-sulting from separation. The. invention isnot limited to waveguidesbutamay also beused with coaxial lines. I

Since many: Qhangescouldbemadein the above ructi a d many ap ren y delydin rs e em ments Qfi h -s inv ntione uld'. bema e W hout depa ti romthe-scope thereo itzis intendedthat all; matter-contained the above.

desc ip i or: shown hth accompa yi g d aw-' i s shall be: terp ted aiilu trati e-a dxnht other and centered in the same transverse planerelative to the longitudinal axes of the wave guides.

2. Av wide band directional coupler comprising a pair of rectangularhollowwave g-uides exe tending, in parallel relationship with v a commonbroad wall therebetween, said; common broad wall having first andsecond, separate openings therein centered along ajline, extending in arectio p rpe i ar. t e ng tu inal ax 'sei. each of said wave guides, thesecond opening. be,- ing an elongated slot having its longitudinalaxisaligned with the center'oi said first opening, and a. co ductive pro e lment xtend ng throu h said first pe ing a diproiec g a apprecia e d anceint th nte io o each oi aid ere,

' guides. th en s o sa d. pro e: el ment bei g spaced, from the. Wallsof therespeotiye Wave guide thev Probe. lement. bein unhnt ed hrandinsulated fr m. sa d cm moh r adwal 3. A Wide band directionalcoupler compr References Cited in the file of this patent UNITED STATESPATENTS Number Name Date Korman July 1, 1947 Sontheimer July 1, 1947Landonv July 8, 1947 Bradley June 14, 1949 Purcell Aug. 9, 1949 TileyAug. 23, 1949 Bethe Aug. 22, 1950 Watson Nov. 6, 1951 Doherty et al Nov.20, 1951 Hansen A Jan. 1, 1952

